H. ducreyi makes a secreted cytolethal distending toxin that causes cytopathic effect on cultured human keratinocytes and fibroblasts. We identified the gene cluster responsible for production and secretion of cytolethal distending toxin, designated cdtABC, and constructed an isogenic H. ducreyi mutant in the structural cdtC gene. The mutant lacks cytolethal distending toxin activity. The purpose of this study is to test the hypothesis that cytolethal distending toxin mutant is impaired in its ability to infect human skin when compared to its isogenic parent. To test this hypothesis, we will compare the ability of the parent and the mutant to cause experimental infection in human subjects. These studies will conclusively establish whether cytoletal distending toxin plays a role in the ability of H. ducreyi to cause pustules.